Bifunctional NiO x /Perovskite Interface Engineering for Efficient Air-Processed Wide-Bandgap Perovskite Solar Cells

Abstract Nickel oxide (NiOx) hole transport layers are widely employed in perovskite solar cells (PSCs) due to their excellent chemical stability. However, the poor quality of the NiOx/perovskite interface limits device performance. Herein, we report a bifunctional interface engineering strategy using ammonium thiocyanate (NH4SCN) that reduces energy barriers and passivates defects at the NiOx/perovskite interface. NH4SCN decreases surface hydroxyl groups on NiOx, suppresses trap states, and improves energy-level alignment of hole transport layer with perovskite. Additionally, NH4SCN promotes the growth of larger perovskite grains, alleviates lattice strain, and passivates defects at buried interface of perovskite film, thus enhancing film quality and improving carrier lifetime. As a result, air-processed wide-bandgap PSCs based on NH4SCN-treated NiOx achieve a power conversion efficiency of 21.41% and an open-circuit voltage of 1.260 V, outperforming control devices (19.81%, 1.236 V). This work provides an effective interface engineering strategy for high-performance wide-bandgap PSCs.